Based on my understanding of your scenario, the problem you’re experiencing might be happening by the fact that
IsNavigationTarget implementation of the INavigationAware interface is returning
True, which means that your target view (EditCustomerView) will be re used and will ensure that only one view will be displayed in the region, in your case the tab control.

On the other hand, you should make sure that your EditCustomerView view is decorated with the
PartCreationPolicy attribute as NonShared. By doing this, a new instance of the exported view model will be created each time it is resolved.

Also take into account that Prism provides the IRegionMemberLifetime interface, which allows you to control the lifetime of views within regions by allowing you to specify whether deactivated views are to be removed from the region or simply
marked as deactivated.

Thank you for your answer, it was very helpful, indeed what was missing was just the PartCreationPolicy attribute.

Actually I had to add the PartCreationPolicy attribute not only to the view, but also to the ViewModel because all Edit Views were sharing the same instance of View Model and consequently showing the same information.